Known in the art is a ball throwing machine (cf. French Pat. No. 2218113, Int.Cl. A 63 B 69/38, 1974), comprising a base, a distributor mounted on the base and designed for a successive supply of balls and also a drive shaft and an impeller with a hammer installed on the drive shaft and designed to strike the ball with the hammer.
The impeller is installed on the drive shaft which is operatively connected to a drive for rotating the impeller in a plane extending at right angles to the shaft axis.
An inclined trough is provided adjacent to the outlet port of the distributor and a follower in the form of a plunger which is designed for feeding a ball from the inclined trough of the distributor to the path of rotation of the impeller so as to strike the ball.
The follower is connected to the impeller by means of a timing mechanism for synchronizing movement of the follower and impeller so as to ensure the feeding of a ball by the follower to the path of rotation of the impeller at an appropriate time moment.
By varying the speed of the shaft with the impeller, the initial velocity of ball projection may be changed.
The prior art ball throwing machine may be effectively used for throwing balls in many applications. It should be, however, noted that in such ball throwing machine a ball is not fixed in the projection position after it has been moved by the follower to the path of rotation of the impeller. Because of the absence of ball retaining at a strictly predetermined point which is most favourable for striking the ball, balls may be hit by the impeller in such a manner as to have various random trajectories and initial velocities.
This is due to the fact that balls have somewhat different resilience and size and the follower speed may be subjected to random fluctuations. Therefore, the direction of projection of balls and their velocity may change arbitrarily during operation of the prior art ball throwing machine. This is not always desirable.
This is especially undesirable in applications where beginners or, the other way round, highly skilled players are to be trained, as well as in simulating champion's strokes, although it might prove desirable in certain applications to use such method of unstable ball throwing, e.g. when it is desirable to have a random nature of projection.
It should also be noted that the random pattern of ball projection practically does not ensure ball projection to various pre-set points of the tennis court at a pre-set velocity. Inaccurate hit of the impeller hammer at the ball results in an increased power consumption by the drive.